1. Field of Invention
The present invention relates to novel methods of preparing fluorinated organic compounds, and particularly to methods of producing fluorinated olefins.
2. Description of Related Art
Hydrofluorocarbons (“HFCs”), in particular hydrofluoro-olefins (“HFOs”) such as tetrafluoropropenes (including 2,3,3,3-tetrafluoropropene (“HFO-1234yf”) and 1,3,3,3-tetrafluoropropene (“HFO-1234ze”)) have been disclosed to be effective refrigerants, fire extinguishants, heat transfer media, propellants, foaming agents, blowing agents, gaseous dielectrics, sterilant carriers, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents, displacement drying agents and power cycle working fluids. Unlike chlorofluorocarbons (“CFCs”) and hydrochlorofluorocarbons (“HCFCs”), both of which potentially damage the Earth's ozone layer, HFCs do not contain chlorine and thus pose no threat to the ozone layer.
Several methods for preparing fluorinated olefins from fluorinated alkanes are known. For example, U.S. Pat. No. 7,560,602 discloses that CF3CF═CHF (“HFO-1225ye”) and HFO-1234yf can be produced via gas phase dehydrofluorination of CF3CHFCHF2 and CF3CHFCH2F, respectively, over a dehydrofluorination catalyst selected from the group consisting of one or more fluorinated metal oxides, metal fluorides, carbon supported transition metals and combinations of these. U.S. Publication No. 2009/0099395 discloses that HFO-1234ze may be produced via gas phase dehydrofluorination of CF3CH2CHF2 by a catalytic process using a zirconium compound-carried catalyst. U.S. Publication No. 2009/0043138 discloses that HFO-1234ze and CF3CH═CF2 (“HFO-1225zc”) may be produced from the dehydrofluorination of CF3CH2CHF2 and CF3CH2CF3 using oxides, fluorides, and oxyfluorides of magnesium, zinc, and mixtures of magnesium and zinc.
Methods for dehydrogenating alkanes into alkenes are known. One such method utilizes mixed metal oxides as dehydrogenation catalysts. For example, U.S. Pat. No. 2,500,920 discloses that chromium oxide catalysts on an alumina support can catalyze dehydrogenation of an alkane to an alkene. Similarly, mixed metal oxide catalysts having Mo—Sb—W or Cr—Sb—W, and at least one metal selected from the group consisting of V, Nb, K, Mg, Sn, Fe, Co, and Ni, can drive oxidative dehydrogenation of propane to propene, as disclosed by U.S. Pat. No. 6,239,325.
Applicants have come to recognize, however, that the above-mentioned mixed metal oxides are not suitable for use in the dehydrogenation of hydrofluorocarbons because of their tendency to react with hydrofluorocarbons, causing the conversion of metal oxides into metal oxyfluorides or even metal fluorides, and the collapse of catalyst structure.
Applicants have also come to recognize that there are significant deficiencies associated with the above-referenced methods, and that such methods are not suitable for producing HFOs such as HFO-1234yf and HFO-1234ze from certain fluorinated alkanes and alkenes. For example, Applicants have found that the dehydrofluorination of 2,3,3,3-tetrafluoropropane (“HFO-254eb”) and 1,3,3,3-tetrafluoropropane (“HFO-254fb”) in the presence of these catalysts forms the byproduct 3,3,3-trifluoropropyne, the toxicity of which is unknown.
Accordingly, Applicants have come to recognize that a need exists for a method of preparing HFOs from fluorinated alkanes, particularly for preparing HFO-1234yf and HFO-1234ze from HFC-254eb and HFC-254fb, whereby the formation of 3,3,3-trifluoropropyne is substantially limited. This invention satisfies this need among others.